1. Field of the Invention
The present invention relates to a differential assembly for a vehicle and more particularly to a differential assembly including an auxiliary gear drive system for supplying additional output torque to a non slipping output shaft of the differential assembly wherein one of the output shafts is slipping and the other of the output shafts is non slipping.
2. Background of the Invention
There are many known differential gear mechanisms in the prior art which are utilized to compensate for slipping of one of the drive wheels of a pair of drive wheels of a vehicle. In a normal or open differential equal torque is provided to a pair of output shafts. The input speed to the differential equals the average output speed of the two wheels. The output speeds of the two wheels are normally equal or substantially equal in normal situations where the vehicle is going in a straight line or slightly turning. In a standard differential when one of the wheels starts to slip relative to the other, such as when the vehicle is stuck, the amount of torque transmitted to the non slipping wheel will decrease due to the fact that the torque delivered by the slipping wheel decreases and equal torque will be provided by the two output wheels. Thus, the standard differential will operate to only transmit the magnitude of torque to the non slipping wheel which is equal to the magnitude transferred to the slipping wheel. Thus, in a slipping situation, the amount of torque delivered to the output wheels is limited to twice the torque being transmitted by the slipping wheel which can approach zero. This is an undesirable situation.
In an effort to solve the problem set forth above, limited slip differentials have been designed. The limited slip differentials allow unequal torques to be transmitted to the two driving wheels. This allows additional torque to be added to the non slipping wheel to allow it to dig in when one of the wheels is slipping. Another differential is disclosed in U.S. Pat. No. 4,077,279 which utilizes a weight member which is actuated by inertial force to trigger locking of the output shafts together upon slipping of a predetermined degree. The use of a locking mechanism which is actuated by inertial force requires the differential gear mechanism to be rotating at a predetermined speed before the inertial force can actuate the locking mechanism.
Another known limited slip differential is disclosed in U.S. Pat. No. 3,448,635, which discloses the use of friction plates to add resistance torque to the slipping output wheel. Adding resistance torque to the slipping wheel enables additional torque to be transmitted to the non slipping wheel due to the fact that equal torque is transmitted to each of the output driving wheels. The use of friction plates causes undesirable heating characteristics and undesirable wear characteristics in the limited slip differential.
Another known differential mechanism is disclosed in Great Britain patent specification No. 183,712, having an application date of July 27, 1921. The British patent specification discloses a differential gear mechanism which provides for a predetermined maximum difference in the relative speeds of the two output members and includes control means which are actuated to prevent any further difference in the relative speed of the driven members when the predetermined maximum difference is sensed.